Table of Contents
In this article we will discuss trapezoidal footing.
Trapezoidal footing is a type of footing that carries unequal loads from 2 columns when the heaviest load outside the column distance is limited.
It is used when the area of footing is fixed and the soils at the site are loose soil.
2. Formula for Calculating Trapezoidal Footing Volume
As we know that, Trapezoidal footing is made by the superimposing of a rectangular cuboid and truncated pyramid as shown in the figure below.
The volume of trapezoidal footing=Volume of Rectangular cuboid (V1) + Volume of a truncated pyramid (V2)
= V1 + V2 …………….(Eq.1)
I. Volume of rectangular cuboid (V1);
= A * B * hc …………….(Eq.2 )
A= length of the cuboid
B= Breadth of cuboid
hc= Height of cuboid
II. Volume of truncated pyramid ( V2 );
= ht/3 * ( A1 + A2 + √(A1 +A2) ) ……..(eq.3)
A1= area of a bottom surface of the truncated pyramid
A2= area of the upper surface of the pyramid
ht= height of the pyramid
From equation 1,2 and 3 we can write the final formula for calculating volume of trapezoidal footing as shown below;
= V1 + V2
= ( A*B*hc) + ht/ 3 ( A1 + A2 + (√ (A1+A2)) )
Now ,We are going to find out the volume of trapezoidal footing shown in figure 3 as above;
i. ht=300mm = 0.3m
ii. hc=300mm=0.3m ( lets assume)
iii. Area of cuboid (A *B)= (2000mm * 1600mm) = 3.2 m²
iv. Area of bottom surface of the pyramid(A1) =3.2m²
v. Area of top surface of the pyramid (A2)= (800*800)mm^2=0.64m²
Now, Total Volume= V1 + V2
=( A*B*hc) + ht/ 3 ( A1 + A2 + (√ (A1+A2)) )
=(3.2 * 0.3) + 0.3/3 (3.2+0.64 +(√(3.2+0.64)))
= 1.539959 m^3
The total volume of the trapezoidal footing of figure 3 = 1.5399m^3
Trapezoidal footing is use
I. For residential house and building.
II. When load applied is uneven or unequal.
III. The soil at the site is loose.
a. Concrete uses are less.
b. Cheap to construct.
c. Less reinforcement is needed.
a. Good for small buildings only.
b. Chance of settlement.
c. Foundation subjected to pull out, torsion, moment.
|Read More: Continuous Footing|
|Read More: Shallow Foundation|
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